1. Field of the Invention
The present invention relates to a zoom lens system suitable for a video camera and an electronic still camera using a solid-state imaging device and the like.
2. Related Background Art
A lot of zoom lens systems suitable for a video camera and an electronic still camera using a solid-state imaging device and the like as an imaging medium have been proposed. Among them, it has been known that those having a high zoom ratio of five or more are constructed by five lens groups or more and have such lens type that the most object side lens group has positive refractive power as described in Japanese Patent Application Laid-Open No. 2002-98893.
On the other hand, a high zoom ratio zoom lens system has a problem that a camera shake caused by a photographer tends to occur on the telephoto side. In order to avoid degradation in the shot image caused by the camera shake, various methods for canceling the image blur caused by the camera shake by shifting an image by means of shifting a portion of the optical system substantially perpendicularly to the optical axis have been proposed. Moreover, a lot of optical systems equipped with such vibration reduction mechanism have been proposed as shown in Japanese Patent Application Laid-Open No. 2003-207715.
In a video camera or an electronic still camera using a solid-state imaging device and the like, recent trend of increasing the number of pixels is continuing, so that higher optical performance is strongly required for a shooting lens. In view of convenience for shooting, a high-zoom-ratio zoom lens is strongly required and in view of portability, compactness is also strongly required. Although both of these requirements have to be satisfied simultaneously, in the zoom lens systems disclosed in Japanese Patent Application Laid-Open No. 2002-98893, optical performance is not sufficiently high over entire focal length range from the wide-angle end state to the telephoto end state and although a high zoom ratio is secured, compactness is not sufficient.
On the other hand, while the request for the function of canceling a camera shake recently becomes high, in the zoom lens systems disclosed in Japanese Patent Application Laid-Open No. 2003-207715, optical performance is not sufficiently high over entire focal length range from the wide-angle end state to the telephoto end state and optical performance upon shifting a portion of the optical system substantially perpendicularly to the optical axis is not sufficiently high. In addition, the zoom ratio is not sufficient since it is less than five.
Although various zoom lens systems of this kind have been proposed in Japanese Patent Application Laid-Open Nos. 2004-252196, 10-260356, 11-23969, 2000-298235, and 2003-177318, any one of them has satisfied not all requirements such as a sufficient zoom ratio, an enough angle of view in the wide-angle end state, compactness, and good optical performance.